In the electronics industry, a continuing objective is to further and further reduce the size of electronic devices while simultaneously increasing performance and speed. Cellular telephones, personal data devices, notebook computers, camcorders, and digital cameras are but a few of the consumer products that require and benefit from this ongoing miniaturization of sophisticated electronics.
Integrated circuit (“IC”) assemblies for such complex electronic systems typically have a large number of interconnected IC chips. The IC chips, commonly called dies, are usually made from a semiconductor material such as silicon or gallium arsenide. Photolithographic techniques are used to form the various semiconductor devices in multiple layers on the dies.
Dies are encapsulated in a molded plastic package that has connectors or leads on the exterior of the package that function as input/output terminals for the die inside the package. The package includes a substrate, a die mounted on the top surface of the substrate, and a heat spreader mounted on the substrate and covering the die.
The substrate may be comprised of a flexible resin tape, a rigid fiber-glass/copper sheet laminate, a co-fired ceramic coupon, a flexible metal lead frame, a ball grid array substrate or other well-known types of substrates in the semiconductor industry, depending on the particular type of semiconductor package being used.
The die is conventionally mounted to the top surface of the substrate with, for example, a layer of an adhesive or an adhesive film, and then electrically connected to the substrate by a number of fine, conductive wires, typically gold (Au) or aluminum (Al), that electrically connect the die to the substrate. The wires are attached to the die at the bonding pads of the die, which are located around the periphery of the die.
The heat spreader is made of a thermally conductive material, usually metal, to improve heat transfer. The heat spreader, covering the die and conductive wires, is attached to the substrate with an adhesive, a thermal paste, or grease. To prevent electrical interference and short circuits, the heat spreader does not touch the die or the conductive wires. Thus, a heat spreader cavity is formed under the heat spreader.
After the heat spreader is attached, the die, the substrate, the heat spreader, and the conductive wires are encapsulated in a mold compound, such as plastic or epoxy, or in a multi-part housing made of plastic, ceramic, or metal. The encapsulation protects the substrate, the heat spreader, the fine conductive wires, and the die from physical, electrical, moisture, and/or chemical damage.
The encapsulation process begins by placing a mold over the die, the substrate, the heat spreader, and the conductive wires. Next, a mold compound is injected into the mold. The mold compound flows through the mold, encasing the die, the substrate, the heat spreader, and the conductive wires.
In order for the heat spreader to efficiently transfer heat, and for the mold compound to protect the die, the substrate, the heat spreader, and the conductive wires, the mold compound must fill the mold and the cavity under the heat spreader. Thus, air must be removed from the mold and from under the heat sink. However, efficient, simple, and cost effective air removal under the heat sink continues to remain a problem during the encapsulation process. In view of the ever-increasing need to save costs and improve efficiencies, it is more and more critical that answers be found to such problems.
Solutions to these problems have been long sought but prior developments have not taught or suggested any solutions and, thus, solutions to these problems have long eluded those skilled in the art.